Magnetic pumping allows the transfer of energy from magnetosonic waves (low frequency, compressive) at magnetohydrodynamical (MHD) scales, to electrons at kinetic scales in space plasmas. This can lead to significant localized heating of ambient electrons in planetary magnetospheres, and has been seen at induced (Mars, Venus) and intrinsic (Earth) magnetospheres. At Mars, the smaller scale size of the induced magnetosphere means that the underlying low frequency waves that drive the pumping can propagate into the planetary ionospheres, where the process can heat ionospheric electrons. The process can thus couple the solar wind to the ionosphere, where it can drive processes such as atmospheric loss to space via enhanced ambipolar electric fields.  

At Mars, pumping events have been identified using MAVEN data, which can resolve the MHD scales of this process. At Earth, MMS can resolve the kinetic scale physics, allowing more detailed analysis into magnetic pumping. Comparisons between the two planets allow conclusions to be drawn about the similarities and differences between this process at induced vs intrinsic magnetospheres. We present detailed case studies of magnetic pumping at both Mars and Earth.

How to cite: Regan, C., Fowler, C., Agapitov, O., and Ledvina, S.: Magnetic Pumping in Planetary Magnetospheres: Comparisons at Mars and Earth, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-135, https://doi.org/10.5194/epsc-dps2025-135, 2025.

On 18 February 2025, Solar Orbiter conducted its fourth Venus gravity assist manoeuvre, reaching a closest approach altitude of 378 km. This was significantly deeper than during previous flybys and brought the spacecraft into the topside ionosphere for the first time. The magnetometer (MAG) and Radio and Plasma Wave (RPW) instruments operated in burst mode during most of the flyby, providing high time resolution measurements. Solar Orbiter approached Venus from the tail region and entered the plasma environment without detecting a clear inbound bow shock crossing. The upstream solar wind appeared steady and calm, as inferred from stable magnetosheath conditions. The ionosphere was encountered in an unmagnetized state, characterized by generally weak magnetic fields in the ionosphere. Two ionopause crossings were observed, one inbound and one outbound, clearly seen in magnetic field, electric field and plasma density data. High-time-resolution electron density measurements, derived from spacecraft potential sampled at 256 Hz and calibrated using the plasma frequency line, revealed fine structure at the ionopause boundary on spatial scales of ~10 km. This is comparable to the local O⁺ inertial length, suggesting the influence of kinetic processes such as ion-scale waves or current sheets. The peak electron density during the flyby reached approximately 2x10⁴ cm⁻³, corresponding to a spacecraft potential of about –45 V. Assuming pressure balance between external magnetic pressure and internal thermal pressure at the ionopause, the electron temperature is estimated to be around 0.6 eV. Near closest approach, approximately 15 magnetic flux ropes were observed, identified by strong peaks in magnetic field magnitude and characteristic rotations in LMN coordinates. These structures were accompanied by simultaneous electron density depletions. Applying a pressure balance assumption across the flux ropes (noting that this may not always be valid) yields an upper limit on the electron temperature of 0.8–2.0 eV within these features. On the outbound leg, Solar Orbiter passed through a still stable dayside magnetosheath and eventually crossed a quasi-perpendicular bow shock.

How to cite: Edberg, N. and the Solar Orbiter RPW & MAG team: Solar Orbiter in Venus ionosphere: results from the 4th flyby, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-302, https://doi.org/10.5194/epsc-dps2025-302, 2025.

Introduction

Mars does not have a global dipole magnetic field as is the case for Earth, but it possesses localized remanent magnetic fields originating in the Martian lithosphere, which are universally accepted to have been generated by an ancient core dynamo. Satellite measurements over the past few decades have provided the necessary data for modeling these crustal fields. The most widely used crustal magnetic field models include the Equivalent Source Dipole (ESD) model and the Spherical Harmonic (SH) model.

Data Sets and Data Selection

Mars Global Surveyor (MGS) operated in Martian orbit from 1997 to 2006, providing magnetic field measurements during two distinct mission phases: the aerobraking and science phase orbit (AB/SPO, 1997-1999) with elliptical orbits, and the mapping phase orbit (MPO, 1999-2006) with near-circular orbits at approximately 400 km altitude. MAVEN (2014–present) and Tianwen-1 (2021–present) continue to operate in elliptical orbits, conducting magnetic field measurements at lower altitudes.

A key challenge in crustal field modeling is minimizing external field interference associated with solar wind interactions with Mars. Langlais et al. (2019) selected MPO datasets with minimal deviation from the mean to construct a preliminary model, and excluded MAVEN datasets with correlation coefficients below 0.4 when compared to the extrapolated field of the preliminary model. Gao et al. (2021) selected MAVEN datasets based on upstream solar wind conditions, retaining orbits when the mean interplanetary magnetic field (IMF) magnitude is below 2.6 nT. Since mean-based criteria for near-circular orbits are physically less reliable than upstream solar wind criteria for elliptical orbits, we decided to use only elliptical orbit data, refine the quiet-period identification method, and incorporate updated MAVEN and Tianwen-1 observations to develop a new crustal field model.

We utilized datasets from MGS during AB/SPO phase (1997-1999), MAVEN (2014-2024), and Tianwen-1 (2021-2023), with the following selection criteria applied to constrain the datasets:

• The bow shock crossings of MAVEN from 2014 to 2022 were identified using the dataset provided by Wedlund et al. (2022), while those for other orbits were manually determined by examining magnetometer measurements. Quiet orbits were selected based on specific criteria: solar wind duration exceeding 0.5 hours, IMF strength below 3 nT, IMF fluctuation rate under 0.3 nT/s, electron density below 0.3 cm⁻³, and solar wind dynamic pressure below 6 nPa. For MGS and Tianwen-1, which lack electron density and dynamic pressure measurements, only the IMF criteria were applied. Only periapsis data from these quiet orbits were retained. Since the operational periods of MAVEN and Tianwen-1 overlap, if one spacecraft detected quiet solar wind conditions within a two-hour window, the periapsis data from the other spacecraft were also retained.
• Due to greater solar wind interference on the dayside, we exclusively utilized data acquired below 350 km altitude on the dayside and below 500 km on the nightside.
• A 60-second moving average was applied to suppress high-frequency noise.
• Following the method described in Langlais et al. (2019) Appendix B, we performed data selection along orbits with increased sampling density in regions exhibiting strong magnetic field gradients or at lower altitudes.

Finally we obtained 0.38 million data points of the field vector, 10% for model assessment and 90% for model construction.

Model Results

In this study, we employ the ESD modeling approach, which imposes less stringent requirements on the spatial uniformity of datasets. Then we used the ESD-derived spatially uniform magnetic field data to construct an SH model, enabling extrapolation to the surface. The calculated field distributions are shown in Figure 1.

Figure 1. Maps of the Martian magnetic field calculated by our SH model at an altitude of 200 km. (a) Br, (b) B_θ , (c) B_φ .

The model performance was evaluated using residuals between the assessment dataset and model predictions. As shown in Figure 2, our model demonstrates superior fitting performance compared to previous studies, indicating that the methodological improvements have enhanced model quality.

Figure 2. Residual distribution of the Langlais et al. (2019) model, the Gao et al. (2021) model, and this model for the assessment datasets.(a) Br, (b) B_θ , (c) B_φ .

Subsequent research will further refine the solar wind selection parameters to enhance model performance, and will consider incorporating relevant studies on the Martian ionospheric current system to optimize the quiet data selection method.

How to cite: Wanqiu, F., Long, C., and Yuming, W.: Modeling the Martian Crustal Magnetic Field Using Data from MGS, MAVEN, and Tianwen-1, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-572, https://doi.org/10.5194/epsc-dps2025-572, 2025.

The composition of Mars' ionosphere has been extensively characterized by MAVEN/NGIMS, and numerous photochemical models have been developed to replicate ion densities in Mars' dayside ionosphere. The molecular dication CO₂⁺⁺ has, as previously reported, been detected and modeled in Mars’ ionosphere; however, previous works have significantly underestimated the observations. In contrast, the noble gas ion Ar⁺ has received limited attention in photochemical modeling studies. In this study, we focus on modeling CO₂⁺⁺ and Ar⁺ and in Mars' dayside ionosphere. For CO₂⁺⁺, an extended lifetime against natural dissociation compared to what is used in earlier modeling works significantly reduces discrepancies between photochemical model predictions and MAVEN observations throughout the altitude range 160-220 km. Our findings indicate that the natural lifetime of CO₂⁺⁺ may require re-evaluation, which is not in conflict with results from a frequently cited experimental investigation. For Ar⁺, we perform both orbital and statistical comparisons between model results and observations and found reasonable model-observation agreement, particularly at altitudes below 200 km, using a higher rate coefficient for the reaction between Ar⁺ and CO₂, and under high solar EUV conditions.

How to cite: Cheng, L., Vigren, E., Persson, M., Gu, H., Cui, J., and Lillis, R.: Photochemical Modeling of CO2++ and Ar+ in the Martian Ionosphere, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-663, https://doi.org/10.5194/epsc-dps2025-663, 2025.

Mars does not possess a significant, global magnetic field, and the solar wind subsequently interacts with
the gravitationally bound and electrically conducting ionosphere. This interaction produces an induced
magnetosphere, within which a plethora of dynamic processes can be active. This study focuses
specifically on the generation, propagation and impact of magnetosonic waves, which can transport
energy through the magnetosphere and into the planetary ionosphere. While these waves have been
observed by orbiting spacecraft (in particular, Mars Atmosphere and Volatile EvolutioN (MAVEN), a
satellite that has been in Mars orbit since 2013), these single point in-situ observations cannot provide
instantaneous coverage of the entire magnetosphere, thus limiting our knowledge of these waves and their
impact on the system. This work utilizes global hybrid simulations of the Mars-solar wind interaction,
specifically from the HALFSHEL code. “Complete” ion physics are included in the simulation code such
that the induced magnetosphere, magnetosonic waves and their propagation, are self consistently
captured. The code can thus be used to identify the generation mechanisms of these waves, their
propagation through the magnetosphere, and where energy carried by these waves is deposited in the
system. These features can be tracked in the full 3D spatial domain, and through time. The preliminary
results from this study are presented, focusing on the initial identification of magnetosonic waves in the
magnetosphere. Their characteristics are compared to those observed by single point MAVEN
measurements.

How to cite: Cupp, S., Fowler, C., and Ledvina, S.: The generation, propagation, and impact of magnetosonic waves in the Mars magnetosphere: analysis of global hybrid simulations, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-762, https://doi.org/10.5194/epsc-dps2025-762, 2025.

Fig. 1: Venus ionosphere observed by VEX VeRa for solar zenith angles (SZAs) on the (a) dayside, (b) terminator, and (c) nightside.The horizontal dashed line indicates the lowest valid altitude of the ionospheric observation.

The Venus Express (VEX) spacecraft orbited Venus from 2006 to 2014. The VeRa experiment [1] onboard VEX utilized radio science techniques to investigate the planet’s ionospheric electron density as well as the pressure, density and temperature of the lower neutral atmosphere.

Figure 1a presents a typical profile of the undisturbed dayside ionosphere of Venus. The lower ionosphere is dominated by photochemical processes and characterized by two major features. The ionospheric peak region (V2) mainly results from photoionization by solar EUV irradiation, while the weaker secondary V1 region originates from the primary and secondary ionization caused by solar X-rays [2]. The electron density of the lower dayside ionosphere shows a strong dependence on solar irradiation at wavelengths shorter than 95 nm [3]. Close to the planetary terminator, VeRa observes a substantial ionosphere (Fig. 1b) where the individual V2 and V1 regions can still be distinguished. On the deep nightside, VeRa observations reveal highly variable ionospheric structures when the noise level of the observations is low (Fig. 1c).

In this study, 9 years of VEX VeRa observations are used to investigate the variability of the Venus ionosphere across the dayside, terminator, and nightside regions. The derived ionospheric properties are compared with accompanying measurements of the solar wind dynamic pressure (from VEX ASPERA4 [4]), solar irradiation flux (FISM V2 model [5]), and results from a ray-tracing analysis, in order to improve our understanding of Venus’ ionospheric variability.

.

References

[1] Häusler et al. (2006)  PSS 54 (13-14)

[2] Fox (2007)  PSS 55 (12)

[3] Peter et al. (2014)  Icarus 233

[4] Barabash et al. (2007)  JGR Planets 112 (E4)

[5] Chamberlin et al. (2020) Space Weather 18 (12)

How to cite: Peter, K., Pätzold, M., Tellmann, S., Oschlisniok, J., Futaana, Y., and Häusler, B.: Exploring the variability of the Venus ionosphere with the Venus Express VeRa radio science experiment, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1267, https://doi.org/10.5194/epsc-dps2025-1267, 2025.

Fig. 1: MEX MaRS observation of (a) the extended Mars dayside ionosphere on Day of Year (DoY) 102 (2019) and (b) the compressed dayside ionosphere on DoY 100 (2021). Grey crosses are the original data points, while the blue line indicates the smoothed data. The vertical grey line indicates the 1ˑσ noise level of the observation.

The Mars Express (MEX) spacecraft has been orbiting Mars since December 2003. Its MaRS (Mars Radio Science) experiment uses spacecraft-Earth radio occultations to provide information about the ionospheric electron density and the pressure, density and temperature of the lower neutral atmosphere. However, due to geometrical constraints, these remote-sensing observations are never accompanied by simultaneous in-situ observations at the same position from MEX itself.

Since the arrival of the MAVEN spacecraft in 2014, new opportunities have emerged to complement MEX MaRS data with in-situ observations. This study compares the coordinates of MEX MaRS dayside ionospheric occultation events (from 2014 through the end of 2022) with MAVEN's pericenter positions to identify instances where the two datasets are spatially and temporally comparable.

The analysis shows that opportunities where MEX MaRS and MAVEN pericenter observation are comparable, are extremely rare. This work presents a detailed case study of two events where meaningful comparisons can be made under the condition that the planetary ionosphere remained sufficiently stable (Fig. 1).

Combining MEX radio science observations with MAVEN's in-situ data enables more comprehensive scientific insights into Martian ionospheric dynamics—insights that are otherwise difficult to obtain. Future and proposed multi-spacecraft missions like EscaPADE and M-MATISSE will be instrumental in expanding our understanding of planetary environments through coordinated observations.

How to cite: Peter, K., Fowler, C., Pätzold, M., Andersson, L., Ramstad, R., Tellmann, S., and Holmström, M.: Multi-spacecraft observations of the Mars dayside ionosphere: a case study with MEX and MAVEN, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1289, https://doi.org/10.5194/epsc-dps2025-1289, 2025.

Abstract: The European Space Agency’s (ESA) Mars Express (MEX) mission to Mars has been returning valuable scientific data for 21+ years.  This data is available to the public for free via the Planetary Science Archive (PSA), which houses the raw, calibrated, and higher-level data returned by the ESA’s planetary missions, including data provided by the various MEX instrument teams.  The Analyzer of Space Plasma and Energetic Atoms 3 (ASPERA-3) has provided several types of datasets throughout the mission, focusing on the ions and electrons in Mars' ionosphere as well as out into the solar wind environment surrounding Mars.

      For the Ion Mass Analyzer (IMA) subinstrument, the ASPERA-3 team has provided new level 4 and level 5 datasets which cover nearly the entirety of MEX's mission lifetime.  The level 4 sets contain data products covering the differential number flux of H⁺, He⁺⁺, O⁺, and O₂⁺ (in units of m^-2 s^-1 sr^-1 eV^-1) for the various sectors of the IMA detector.  The level 5 sets contain data products combining all the IMA sectors' data to yield temperature (eV), density (cm^-3), and velocity (km s^-1) information on these same 4 ion species.  All this data and more can be accessed at the PSA at: https://archives.esac.esa.int/psa/

Mars Express: MEX was inserted into Mars orbit in December 2003, though several instrument test observations also exist from the cruise phase of the mission, prior to arrival at Mars.  Thus, this long-lived Mars mission covers 21+ years of data with its 7 instruments.  Later in the mission’s lifetime, the camera used for the Beagle 2 lander separation was reactivated and used for public outreach.  Over time, the camera began to be used for scientific observations as well, making  MEX an unusual mission in that with this addition of the VMC instrument it now has more scientific instruments in operation than it was launched with.

The PSA user interface: The ESA’s PSA uses the Planetary Data System (PDS) format developed by NASA to store the data from its various planetary missions.  In the case of MEX, the data is stored in the PDS3 format, which primarily uses ASCII files to store and describe the data.  Newer missions, from ExoMars onward use the PDS4 data standard, which uses XML files to store the label information. 

       There are three primary ways in which to find the data.  One is the FTP area, which houses all the public data in the PSA.  Here, there are no advanced search capabilities, but it does provide access to all the supporting files and documentation for the various datasets.  When first searching for new data, users would benefit from using the Table View search interface [1].  Here the user can search using various parameters, such as mission name, target, instrument name, processing level, observation times, etc.  The Table View is also linked to the Image View, where users can view the browse images provided by the PI teams.  The Table View interface also has a section for “Free Search”, allowing one to use Contextual Query Language (CQL) to search over additional parameters.  These various search methods rely in part on the metadata provided by the instrument teams in the labels associated with each of the data products.

       Finally, there is also a Map View for viewing the footprints of data from those instruments where such calculations can be of some utility.  This Map View is built using GIS tools.

Conclusion: The delivery of the ASPERA-3 data provides new high level data on the ion populations in the vicinity of Mars.  This data can be freely accessed at the ESA’s PSA, at https://archives.esac.esa.int/psa/.  There are multiple ways of browsing the ASPERA-3 and other instrument teams’ data, including from other planetary missions, which will be explained in this poster.  The development of the PSA’s user interface is an ongoing project, and we welcome feedback from the community for suggestions on new ways to search this wealth of data.  Feedback and suggestions can be sent via our Help Desk system at:

https://support.cosmos.esa.int/psa/

Acknowledgements: The MEX Support Archive Scientists and the entire PSA team would like to extend their thanks to the ASPERA-3 team for their effort in continuing to deliver new data from Mars to the public via ESA’s PSA.  Our thanks go also to the European taxpayers, whose contributions to the European Space Agency enable the gathering and dissemination of this scientific knowledge, and preserving it for future generations of scientists to work on.

References: [1] Besse S. et al. (2018) Planetary and Space Science, 150, 131-140.

How to cite: Grotheer, E., Holmstroem, M., Williamson, H., Breitfellner, M., Godfrey, J., Heather, D., Martin, P., Wilson, C., Coia, D., Lim, T., Bentley, M., De Marchi, G., Merin, B., Cornet, T., Docasal, R., Oliveira, J., Osinde, J., Raga, F., Ramos, G., and Trejo, A.: New MEX-ASPERA-3 Ion Mass Analyzer High-Level Data In The ESA's Planetary Science Archive, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1321, https://doi.org/10.5194/epsc-dps2025-1321, 2025.

The nightside ionosphere of Mars is formed by plasma transport from the dayside and electron precipitation. Significant progress has been made in our understanding of its composition and structure at low altitudes. However, what happens at higher altitudes remains unclear. Plasma structures escaping from the nightside of Mars could reveal the plasma transport paths from the dayside and from the nightside to space. Moreover, the response of escaping plasma structures to changing solar wind conditions will shed light on the dynamic evolution of the system. Mapping the paths of escaping plasma structures will result in a better understanding of the evolution of atmospheric escape at Mars and the contribution of escaping plasma structures to the total atmospheric loss. In this study we probe escaping plasma structures utilising two special campaigns of ESA's Mars Express mission as well as observations from NASA's MAVEN mission, in the high-altitude nightside ionosphere of Mars. Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) is the radar on board Mars Express and samples the ionosphere at altitudes no higher than ~1500 km. However, in our study we look at observations from consecutive orbits during two special MARSIS campaigns, each consisting of 5 orbits, that took place in September 2023 and April 2024, for which MARSIS was operated at altitudes up to ~5000 km. 
We see a variable nightside ionosphere at high altitudes that changes between consecutive MEX orbits. MARSIS detects plasma structures appearing at different altitudes or disappearing between orbits. We compare with MAVEN measurements to better evaluate both the escaping plasma structures and the solar wind conditions. MAVEN too sees plasma structures at high altitudes on the nightside, changing between orbits, confirming the variability of the high-altitude nightside ionosphere and revealing a dusk-dawn asymmetry in the observed electron densities.
 

How to cite: Stergiopoulou, K., Lester, M., Joyce, S., Andrews, D., Edberg, N., Persson, M., Xu, S., Romanelli, N., Curry, S., Holmström, M., Fowler, C., Ma, Y., Ramstad, R., Kim, K., Sánchez-Cano, B., Aizawa, S., and Cicchetti, A.: Escaping plasma structures in the Martian magnetotail as observed during two special MARSIS high-altitude campaigns, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1420, https://doi.org/10.5194/epsc-dps2025-1420, 2025.

We statistically analyze the power spectral density (PSD) of magnetic field turbulence in the upstream solar wind of the Martian bow shock by investigating the data from Tianwen-1 and MAVEN during November 13 and December 31, 2021. The spectral indices and break frequencies of these PSDs are automatically identified. According to the profiles of the PSDs, we find that they could be classified into three types: A, B and C. Only less than a quarter of the events exhibit characteristics similar to the 1 AU PSDs (Type A). We observe the energy injection in more than one-third of the events (Type B), and the injected energy usually results in the steeper spectral indices of the dissipation ranges. We find the absence of the dissipation range in over one third of the PSDs (Type C), which is likely due to the dissipation occurring at higher frequencies rather than proton cyclotron resonant frequencies. We also find that the two spacecraft observed different types of PSDs in more than half of the investigated episodes, indicating significant variability upstream of the Martian bow shock. For example, the Type-B PSDs are more often seen by Tianwen-1, which was near the flank of the bow shock, than by MAVEN near the nose. This statistical study demonstrates the complicated turbulent environment of the solar wind upstream of the Martian bow shock.

How to cite: Zou, Z., Wang, Y., and Su, Z.: Statistical Study on the Solar Wind Turbulence Spectra upstream of Mars, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-214, https://doi.org/10.5194/epsc-dps2025-214, 2025.

When the magnetized solar wind plasma encounters a non-magnetized planet, electrical currents will be induced in the ionosphere and in the deflected plasma, forming an induced magnetosphere. 
As an example of a non-magnetized planet, we model the interaction between Mars and the solar wind using a hybrid plasma model (ions as particles, electrons as a fluid). 
We investigate the morphology of the current systems at Mars, and how they depend on upstream solar wind conditions.  Currents in the bow shock, in the magnetosheath, and in the ionosphere, are mapped.  We also study the coupling and closure of the currents and draw conclusions for other non-magnetized planets.  

How to cite: Holmstrom, M.: Current systems at non-magnetized planets, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-517, https://doi.org/10.5194/epsc-dps2025-517, 2025.

Understanding the dynamics of the Venusian atmosphere in the 90–110 km altitude range is critical for investigating the coupling processes between the neutral atmosphere and the lower ionosphere. Recent studies suggest that near-infrared heating due to CO₂ absorption at the subsolar point leads to significant temperature enhancements in this region ( Gilli et al., 2017). However, direct observations remain limited.

In this study, we present a new approach to estimate the neutral temperature in the atmospheric-ionospheric transition region of Venus. Assuming the atmospheric composition up to 110 km is primarily dominated by CO₂ and N₂, and that the atmosphere is in hydrostatic equilibrium, we retrieve temperature profiles from radio occultation data. As this shows a significant presence of plasma, its contributions to the radio signal are mitigated using dual-frequency measurements for Venus Express (VEX) data, while for single-frequency observations, a one-dimensional photochemical model (1D-PCM, Ambili et al. 2024) is employed to simulate and subtract the plasma effect. A boundary temperature of 200 K and 240 K at 110 km altitude is assumed based on previous model predictions (Navarro et al., 2021; Ponder et al., 2024), and the temperature profile is subsequently derived using the hydrostatic framework (Imamura et al., 2017).

Figure: The purple curve represents the result from the standard retrieval method, while the green and red curves correspond to outcomes from the newly proposed approach.

Our preliminary results indicate a temperature peak of approximately 330 K near 105 km altitude, with an uncertainty of ~50 K due to the choice of boundary conditions and frequency residual processing. Although the current method and results are early-stage, they show promising consistency with solar occultation observation by VEX (Mahieux et al. 2023), and further refinements will be presented at the conference.

Acknowledgment: This work was supported by the Japan Society for the Promotion of Science (JSPS). We thank Prof. B. Hauesler, the principal investigator of, Venus Express Radio Science payload, for archiving the frequency residual data sets. We also acknowledge the effort of the Akatsuki radio science team in Japan and India for making the dataset available to us.

References:

• Gilli, G., Lebonnois, S., González-Galindo, F., López-Valverde, M.A., Stolzenbach, A., Lefèvre, F., Chaufray, J.Y., Lott, F., 2017. Thermal structure of the upper atmosphere of Venus simulated by a ground-to-thermosphere GCM. Icarus 281, 55–72. http://dx.doi.org/10.1016/j.icarus.2016.09.016.

• Imamura, T., Ando, H., Tellmann, S., Pätzold, M., Häusler, B., Yamazaki, A., Sato, T.M., Noguchi, K., Futaana, Y., Oschlisniok, J. and Limaye, S., 2017. Initial performance of the radio occultation experiment in the Venus orbiter mission Akatsuki. Earth, Planets and Space, 69, pp.1-11.

• Ambili, K.M., Choudhary, R.K. and Tripathi, K.R., 2024. Exploring sensitivity: Unveiling the impact of input parameters on Venus ionosphere V2 layer characteristics. Icarus, 408, p.115839.

• Navarro, T., Gilli, G., Schubert, G., Lebonnois, S., Lefèvre, F. and Quirino, D., 2021. Venus’ upper atmosphere revealed by a GCM: I. Structure and variability of the circulation. Icarus, 366, p.114400.

• Ponder, B.M., Ridley, A.J., Bougher, S.W., Pawlowski, D. and Brecht, A., 2024. The Venus global ionosphere‐thermosphere model (V‐GITM): A coupled thermosphere and ionosphere formulation. Journal of Geophysical Research: Planets, 129(7), p.e2023JE008079.

How to cite: Tripathi, K. R. and Imamura, T.: Thermal Structure of Venus’s Upper Atmosphere (90–110 km) Derived from Radio Occultation Data, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-607, https://doi.org/10.5194/epsc-dps2025-607, 2025.

We make use of photochemical modelling and measurements by the Neutral Gas and Ion Mass Spectrometer (NGIMS) onboard the Mars Atmosphere and Volatile EvolutioN mission (MAVEN) in an attempt to identify the ion species that dominate the sub-population of ions in the Martian ionosphere characterized by a mass of 41 atomic mass units (amu). Previous photochemical reaction networks used for the ionospheres of Mars and Venus include only a single species, namely ArH⁺, to account for ions with that mass. We highlight that the straightforward photochemical modeling of ArH⁺ yields predicted concentrations that are two orders of magnitude lower than the observed 41 amu ions densities in the dayside ionosphere of Mars. We hypothesize that the 41 amu ion population is instead dominated by protonated dicarbon monoxide, HC₂O⁺, and we advocate for experimental investigations into relevant ion-neutral reactions.

How to cite: Cheng, L., Vigren, E., Cui, J., Stone, S., and Benna, M.: Reviewing 41 amu ions in the Martian Ionosphere, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-689, https://doi.org/10.5194/epsc-dps2025-689, 2025.

We calculate unattenuated photoionization and photodissociation rate coefficients using solar spectral irradiance (SSI) measurements from the TIMED/SEE mission (Woods et al., 2005) over a full solar cycle (2004–2014). These coefficients are parameterized by the solar activity index F₁₀.₇P, defined as F₁₀.₇P = ½(F₁₀.₇ + F₁₀.₇A), where F₁₀.₇ (10.7 cm solar radio flux) acts as a proxy for solar extreme ultraviolet (EUV) variability, and F₁₀.₇A represents its 81-day running average. Combining high-resolution (1 nm) SSI data with cross-sections from the PHIDRATES database (Huebner & Mukherjee 2015; http://phidrates.space.swri.edu/), we derive power-law relationships (j = A0[F₁₀.₇P]A1) for 48 reactions involving 12 species critical to Solar System atmospheres and cometary comae: H, H₂, OH, H₂O, O, O₂, C, CO, CO₂, N₂, N, and CH₄. 

Whereas prior estimates are limited to a subset of solar conditions (e.g., solar minimum or maximum), the photo rate coefficients derived here are broadly consistent with those results while extending them to span the full range of solar activity. This work establishes an efficient, observational approach to estimate photoionization rates requiring access to SSI or cross-section data. By utilizing F₁₀.₇P, a widely available and historical solar proxy, the power laws allow for easier modeling of atmospheric and cometary chemistry under diverse solar conditions. Applications include simulating tenuous exospheres (e.g., Mercury, Moon) and analyzing in situ data from outer planets and comets. The method is anchored in publicly accessible PHIDRATES cross-sections and TIMED/SEE SSI records (http://lasp.colorado.edu/home/see/data/daily-averages/level-3), ensuring utility for a variety of studies. Future work will address uncertainties for resolution-sensitive reactions and expand the species/reaction inventory, advancing our capacity to model solar-driven photochemistry throughout the Solar System.

How to cite: Mapaye, R. and Moore, L.: Photoionization and photodissociation rates across a solar cycle , EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-832, https://doi.org/10.5194/epsc-dps2025-832, 2025.

The 3DVI (3-D Velocity of Ions) sensors that are under development for the ESA M7 candidate M-MATISSE mission are designed to address two fundamental questions about the Martian plasma environment:

• How are thermal ions accelerated beyond escape velocity in the ionosphere?
• How is ion escape controlled? Is it source-limited or energy-limited?

To answer these questions, precise measurements of ion bulk parameters in the upper ionosphere, where the initial acceleration processes are ongoing, shall be conducted. Our dedicated low-energy ion sensor will regularly measure the ionospheric thermal ions for the first time at Mars.

Building upon the success of ASPERA-3 on Mars Express as well as other Mars missions, M-MATISSE's 3DVI measurements will provide insights into the Martian upper atmosphere. The simultaneous measurements from two spacecraft with full plasma suites onboard will address energy transfers from the solar wind to the ionosphere. This will allow us to monitor the ionospheric ions in detail, shedding light on the thermosphere-ionosphere coupling that governs the first acceleration of ionospheric ions, which eventually escape to space.

3DVI instrument is based on the well-established techniques of RPA (Retarding Potential Analyzer) and IDM (Ion Drift Meter). The instrument consists of two sensor heads, RPA and IDM. Both have fields-of-view of 45° (half cone), with their boresight directions pointing to the ram direction of the spacecraft. The RPA head is to determine the velocity distribution function along the line of sight by using retarding potential in front of the cathode plate. The IDM head determines the incoming ion directions (i.e., two angles) by measuring the current differences between the prepared cathodes of the sensor. The measurement principle has been used in various space missions since 60–70s, but 3DVI is optimized for the Martian upper ionosphere environment.

In this talk, we will present the scientific background for the 3DVI instrument and report its current design and development status.

How to cite: Futaana, Y., Shimoyama, M., Karlsson, S., Puccio, W., Berglund, M., Wecker, M., Eriksson, A., Andrews, D., Barabash, S., Holmstrom, M., Kim, K., Malatinszky, A., Menpara, N., Ohlsson, D., and Williamson, H.: How do ionospheric ions get escape energy at Mars? M-MATISSE/3DVI science and instrument, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-906, https://doi.org/10.5194/epsc-dps2025-906, 2025.

The structure and dynamics of induced magnetospheres around non-magnetized planets such as Mars and Venus are entirely driven by upstream conditions. These are defined by the solar wind density and velocity, as well as the magnitude and direction of the interplanetary magnetic field (IMF). Certain extreme values of these upstream parameters or specific combinations of them can result in distinct interaction regimes that are morphologically different from the nominal case.

The best-studied examples to date are the degenerate induced magnetosphere (DIM) and the disappearing magnetosphere. The former corresponds to cases where the IMF cone angle is very small (typically <5°-10°), while the latter is associated with extremely low solar wind densities (as low as ~0.05 cm⁻³).

We review extreme cases of morphologically distinct induced magnetospheres, with a focus on the DIM. We also propose a physics-based classification of these extreme cases and outline the main open scientific questions relevant to each category.

Finally, we discuss the importance of studying such interaction regimes, as insights gained may be applicable to understanding:

• Stellar wind–exoplanet interactions
• The space environments of exotic objects (e.g., free-floating planets)
• Past or future solar system conditions
• Moon–magnetosphere interactions around outer planets

How to cite: Barabash, S., Holmström, M., Wang, X.-D., and Zhang, Q.: Extreme induced magnetospheres , EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1394, https://doi.org/10.5194/epsc-dps2025-1394, 2025.

Introduction: Solar flares are among the most powerful manifestations of magnetic activity, characterized by sudden, violent eruptions in the solar atmosphere, ranging from 10¹⁹ erg in nanoflares up to 10³² erg in large two-ribbon flares. Since their first detection (Peterson and Winckler, 1959), a significant body of data have been collected, thanks to the advent of spacecraft observations of solar flares (e.g. OSO 7, Explorer, SMM, GRANAT, ICE/ISEE 3, GOES). The latter enabled detailed statistical investigations of flare properties and underlying physical mechanisms (e.g., Temmer et al. 2001; Veronig et al. 2002; Lee et al. 2012; Joshi et al. 2015).

This work presents a comprehensive statistical analysis of the size and temporal characteristics of soft X-ray (SXR) flares across four solar cycles (SC21–SC24), covering the period from September 1975 to June 2017. More in detail, we investigate the distribution characteristics of solar flares, shedding light on their statistical properties and their relationship with the solar activity. Our analysis provides valuable insights into the distribution patterns, offers estimates for the occurrence of intense solar flare events, and proposes a monitoring framework.

Results: Flare data were obtained from the GOES satellite archive, using the 1–8 Å flux channel to identify start, peak, and end times.

We first explore the relationship between flare occurrence rates and solar activity. Temporal properties (duration, waiting time) and energetic properties (peak flux) are analyzed through their frequency distributions. Results indicate a clear correlation between flare duration and peak intensity with the level of solar activity, while waiting time appears largely uncorrelated.

Additionally, we investigate correlations among these parameters, confirming that flare duration increases with flare importance class. Notably, the distribution of durations for X-class flares reveals a secondary peak at ∼100 minutes for SC21 and SC22 and ∼80 minutes for SC23 and SC24 (Figure 1), referring to extremely long duration events (LDE).

Figure 1. Probability density functions (PDFs) of the observed flare duration data, during SC23 and SC24, compared with fitted unimodal and bimodal distribution models. The red solid line represents the fitted bimodal Gaussian mixture model.

Finally, we assess time–energy correlations in flare sequences to test the hypothesis, proposed by Rosner and Vaiana (1978), that energy builds up progressively prior to major events. Analyzing precursor flares from the same active region preceding X-class events, we find no monotonic increase in energy, suggesting a limited role for precursors in triggering major flares. Overall, no significant correlation is found between waiting time and peak intensity for flares in SC23 and SC24 (Figure 2).

Figure 2. Correlation scatter plot of flare peak-intensity and the waiting time for SC23 (red dots) and SC24 (blue dots).

This study highlights key statistical features of solar flare behavior that may constrain the plausible physical mechanism that generated them. Future work will focus on linking these statistical signatures to the underlying physical processes responsible for flare generation.

References: Joshi, B., Bhattacharyya, R., Pandey, K.K., Kushwaha, U., Moon, Y.-J.: 2015, Evolutionary aspects and north-south asymmetry of soft X-ray flare index during solar cycles 21, 22, and 23. Astron. Astrophys. 582, A4.

Lee, K., Moon, Y.-J., Lee, J.-Y., Lee, K.-S., Na, H.: 2012, Solar Flare Occurrence Rate and Probability in Terms of the Sunspot Classification Supplemented with Sunspot Area and Its Changes. Sol. Phys. 281, 639.

Rosner, R., Vaiana, G.S.: 1978, Cosmic flare transients: constraints upon models for energy storage and release derived from the event frequency distribution. Astrophys. J. 222, 1104.

Temmer, M., Veronig, A., Hanslmeier, A., Otruba, W., Messerotti, M.: 2001, Statistical analysis of solar Hα flares. Astron. Astrophys. 375, 1049.

Veronig, A., Temmer, M., Hanslmeier, A., Otruba, W., Messerotti, M.: 2002, Temporal aspects and frequency distributions of solar soft X-ray flares. Astron. Astrophys. 382, 1070.

Acknowledgements We acknowledge support by the INAF with the mini-grant, ‘Space WEather Analysis of Rogue events (SWEAR)’ (F.O. 1.05.23.04.03).

How to cite: Biasiotti, L. and Ivanovski, S. L.: Statistical Analysis of Solar Flare Properties from 1975 to 2017, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1819, https://doi.org/10.5194/epsc-dps2025-1819, 2025.

The planet Mars does not possess an intrinsic global dipole magnetic field. As a result, the solar wind interacts with the gravitationally bound and electrically conducting ionosphere to form an induced magnetosphere that acts to decelerate and deflect the incident solar wind flow about the planet. An important aspect of such an induced magnetosphere is the “draping” of interplanetary magnetic field lines about the obstacle. This draping can lead to field lines having one end anchored within the planetary ionosphere while the other end connects to the solar wind (then known as “open” field lines). On the nightside of the planet within the magnetotail region, these open field lines can provide a pathway for cold low-energy ionospheric ions to flow tailward and escape to space.

                  The MAVEN spacecraft commonly observes low frequency (<100 Hz) electric field waves in conjunction with this cold ion outflow. In this work, we discuss several characteristics of the observed waves; discuss possibilities for the underlying wave growth mechanism(s), and source(s) of free energy; and evaluate their impact on the outflowing plasma. Candidate instability mechanisms include the two stream instability between outflowing ionospheric protons and heavier O+ and O2+ ions or wave growth due to specific features within the energy and pitch-angle distributions of precipitating sheath electrons: when drawn out of the ionosphere by an ambipolar electric field, for example, the ions will be accelerated through the same electric potential, flowing at the same energy but different velocity, leading to instability.

                  The observed plasma waves coincide with modifications of the ion distribution functions (namely, emergence of energetic tails), suggesting the possibility that the waves act to decelerate protons and accelerate the heavier ions. We evaluate the impact of such a process on heavy ion escape rates. In particular, we evaluate how effective the process can be in shifting the heavy ion distribution function from initially just below escape energy, to just above it.

How to cite: Fowler, C., Akbari, H., and Newman, D.: Plasma instabilities driven by cold ion outflow in the Mars magnetotail region, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-202, https://doi.org/10.5194/epsc-dps2025-202, 2025.